FIELD OF THE INVENTION
This invention relates to a method and apparatus for removal of an implanted object from a patient's body and specifically for removal of transvenous endocardial leads from a patient's heart and the venous paths thereto.
Generally speaking, a lead permits an implantable pulse generator, commonly known as a pacemaker, to stimulate the heart. More specifically an endocardial lead provides an electrical pathway between the pacemaker, connected to the proximal end of the lead, and endocardial tissue, in contact with the distal end of the lead. Endocardial tissue refers to a specific layer of tissue in the interior of the heart's chambers. In such a manner electrical pulses emitted by the pacemaker travel through the endocardial lead and stimulate the heart.
Endocardial leads are often placed in contact with the endocardial tissue by passage through a venous access, such as the subclavian vein or one of its tributaries. Thus a transvenous endocardial lead refers to a pacemaker lead which contacts endocardial tissue through a vein.
In the past, various types of transvenous endocardial leads have been introduced into different chambers of the heart including the right ventricle, right atrial appendage and atrium as well as the coronary sinus. These leads usually are composed of an insulator sleeve that contains a coiled conductor having an electrode tip attached at the distal end. The electrode tip is held in place within the trabeculations of endocardial tissue. The distal ends of many available leads include flexible tines, wedges, or finger-like projections which extend radially outward and usually are molded from and integral with the insulator sleeve of the lead. These tines allow better containment by the trabeculations of endocardial tissue and help prevent dislodgement of the lead tip.
Once an endocardial lead is implanted within a chamber, the body's reaction to its presence furthers its fixation within the heart. Specifically, shortly after placement, i.e. acute placement, a blood clot forms about the flanges or tines due to enzymes released in response to the irritation of the endocardial tissue caused by electrode tip. Over time, i.e. during chronic implantation, fibrous scar tissue eventually forms over the distal end, usually in three to six months. In addition, fibrous scar tissue often forms, in part, over the insulator sleeve within the venous system and the heart chamber. Such tissue fixes the electrode tip within the heart during the life of the lead.
Although the state of the art in implantable pulse generator or pacemaker technology and endocardial technology has advanced considerably, endocardial leads nevertheless occasionally fail, due to a variety of reasons, including insulation breaks, breakage of the inner helical coil conductor thereof and an increase in electrode resistance. Also, in some instances, it may be desirable to electronically stimulate different portions of the heart than that being stimulated with leads already in place. Due to these and other factors, therefore, a considerable number of patients may come to eventually have more than one, and sometimes as many as four or five, unused leads in their venous system and heart.
Unused transvenous leads increase the risk complications will develop. Possible complications associated with leaving unused leads in the heart and venous system include an increased likelihood an old lead may be the site of infection. Development of an infection may, in turn, lead to septicemia, a possibly fatal complication. Unused leads may also cause endocarditis. Furthermore, unused leads may entangle over time, thereby increasing the likelihood of blood clot formation. Such clots may embolize to the lung and produce severe complications or even fatality. The presence of unused leads in the venous pathway and inside the heart can also cause considerable difficulty in the positioning and attachment of new endocardial leads in the heart. Moreover, multiple leads within a vein or artery may impede blood flow causing fatigue, weakness or dizziness within the patient. Further description and detail concerning the complications associated with unused leads left in place may be found in "Lead Extraction", Byrd et al., Cardiology Clinics, Vol. 10, No. 4, November, 1992, incorporated herein by reference.
As serious as the risks associated with leaving an unused lead in place may be, the risks associated with past methods and devices for lead removal were often greater. One technique used to remove a lead was to apply traction and rotation to the outer free end of the lead. This technique, however, could only be done before the lead tip became fixed in the trabeculations of endocardial tissue by large clot development. Clot development, however, is difficult to detect. Even shortly after lead implantation there exists the risk a clot has formed. Removal of a lead at that time may cause various sized emboli to pass to the lungs, possibly producing severe complications.
In cases where the lead tip has become attached by fibrous scar tissue to the heart wall, removal of the lead has presented further major problems and risks. Porous lead tips may have an ingrowth of fibrous scar tissue attaching them to the heart wall. Sufficient traction on such leads in a removal attempt could cause disruption of the wall prior to release of the affixed lead tip, causing fatality. Even if the tines of the leads are not tightly scarred to the heart wall similar risks are faced. Moreover, lead removal may further be prevented by a channel of fibrotic scar tissue and endothelium surrounding the outer surface of the lead body and specifically the insulator sleeve, as mentioned above, at least partway along the venous pathway. Such "channel scar" tissue prevents withdrawal because of encasement of the lead. Continual strong pulling or twisting of the proximal free end of the lead could cause rupturing of the right atrial wall or right ventricular wall. Encasement by fibrous scar tissue in the venous pathway and in the trabeculations of cardiac tissue typically occurs within three to six months after the initial placement of the lead.
The great risks presented by lead removal using traction and rotation techniques are such that if it becomes imperative to remove a lead (as in the case of septicemia) those doctors who have not focused and developed a specialty in lead removal often elect to have the patient's chest opened and the lead surgically removed rather than attempt removal using traction and rotation techniques. Even those doctors who have developed a specialty in lead removal sometimes elect to have the lead surgically removed rather than face the many risks presented.